1. Field of the Invention
The present invention relates to data access control method and apparatus, and more particularly, to data access control method for inserting null packet to increase fluency of media play and corresponding data access control module.
2. Description of the Prior Art
PCMCIA (personal computer memory card international association) cards may be used to decode image. For example, after paying fee to digital television (TV) operator, PCMCIA card equipped with decoder chip would be provided to subscriber. Alternatively, decoder program or serial number would be provided if subscriber already owns PCMCIA card. As a result, TV data encoded by operator could be decoded and played by PCMCIA card.
The classic decoding flow of PCMCIA card could be categorized into two kinds. First, the decoded TV data stream is stored and encrypted again by another encryption method. Once user wants to play, the stored and encrypted TV data stream would be decrypted and played. In this example, the locally encrypted TV data stream is stored in a storage device other than PCMCIA card. It is possible to retrieve the encrypted TV data stream from the separate storage device illegally and to decrypt the encrypted TV data stream illegally. In such architecture, the protection to TV data stream is not very well. In alternative architecture, the encrypted TV data stream is stored without being decrypted. Once user wants to play, the stored encoded TV data stream is sent to PCMCIA card for decoding and play. Since operator is required to provide PCMCIA card or associated information for decoding the TV data stream in the second scenario, the protective strength is stronger than the first one.
Please refer to FIG. 1, which is a block diagram of a digital TV device 100 equipped with PCMCIA card in the prior art. The digital TV device 100 adopted the fore mentioned second mechanism, i.e., the encoded TV data stream is stored without being decoded, is sent to PCMCIA card for decryption, and then is played. As shown in the FIG. 1, the digital TV device 100 comprises an antenna 101, a tuner 103, a demodulator 105, a data access control device 107, and a PCMCIA card 109. The antenna 101 is configured to receive TV data signal comprising signal encoded by the operator. The tuner 103 is configured to tune the frequency to a specified channel. The demodulator 105 receives TV data signal from the tuner 103, demodulates the input signal and performs channel calibration, synchronization, forward error connection, and etc. Because the tuner 103 and the demodulator 105 in the digital TV device 100 are well-known to ordinary skilled in the art, the present invention has no further discussions on them. The original TV data (SD) such as MPEG (Motion Picture Experts Group) transport stream processed by the tuner 103 and the demodulator 105 is transmitted to the data access control device 107. As mentioned above, the original TV data (SD) is stored in the data access control device 107. Once the data access control device 107 receives an output command, the stored original TV data SD′ is outputted to the PCMCIA card 109 for decoding and the decoded TV data CD is generated accordingly. The decoded TV data CD may be sent directly to display or manipulated by some sorts of image processing such as image timing calibration or image contrast enhancement.
A timing alignment mechanism exists in original TV data packets. However, the alignment mechanism fails to function properly because the packets are stored in the storage device. In the architecture discussed above, since the original TV data SD is stored and sent to PCMCIA card 109 for decoding and play, the alignment mechanism of packets is broken. Hence, when user watches the stored original TV data SD′, the fluency, smoothness, and quality of image is not comparable with real time TV data.
From the above it is clear that prior art still has shortcomings. In order to solve these problems, efforts have long been made in vain, while ordinary products and methods offering no appropriate structures and methods. Thus, there is a need in the industry for a novel technique that solves these problems.